1. Field of the Invention
This invention relates to electrical connectors that terminate shielded cable, and more particularly is directed towards means incorporated in an electrical connector receptacle for grounding the shield of the cable.
2. Description of the Related Art
Electrical cables that incorporate one or more shielded conductors are well known. Shielded cable is used, for example, when it is desired to shield a low level, information-bearing electrical signal from spurious external electrical interference. A shield is normally provided by surrounding the information-carrying conductor with a conductive or semi-conductive material that is connected in some manner to a source of ground potential.
Modular plugs and modular jacks are now widely used as general interconnect devices for a variety of types of electrical equipment. As utilized herein, the terms "modular jack" and "modular plug" connote the miniature, quick-connect-and-disconnect jacks and plugs developed by Western Electric Company and Bell Telephone Laboratories originally for use with telephone equipment (see, for example, U.S. Pat. Nos. 3,699,498; 3,850,497; and 3,860,316). The combination of a multi-conductor cable terminated by one or more modular plugs is commonly referred to as a cordset.
A modular jack generally includes a plurality of substantially identical, side-by-side conductors each of which include a spring contact portion that extends into a forwardly positioned plug-receiving cavity. The spring contact portions of the conductors make electrical contact with the upper surface of the substantially planar contact terminals of the modular plug. The plug's contact terminals characteristically include insulation-piercing tangs at their lower edges for terminating the individual wires of the multi-conductor cable.
The conductors of the modular jack generally comprise metal contacts that are stamped and formed from a thin piece of sheet metal. The width of each individual contact, which is substantially flat, may typically be about 0.0175 inch. When such a jack is utilized to directly couple a modular plug or cordset to a printed circuit board, as described, for example, in U.S. patent application Ser. No. 527,852, now abandoned and in U.S. Pat. No. 4,210,376, the width of the flat metal contact is substantially constant along its length (from the spring contact portion at the plug-receiving end to the solder post portion that goes through holes formed in the printed circuit board for subsequent wave-soldering). Alternately, the spring contact portion may be crimped to an insulated wire terminated by a spade lug as set forth in U.S. Pat. No. 3,850,497.
One problem with prior art shielded cables is that, due to bulky metallic shields, they were generally too large to fit within the very limited cable-receiving cavity of a normal modular plug. In U.S. Pat. No. 4,424,403, however, a shielded multi-conductor cable is described which is particularly designed to enable termination of the cable in a miniature, telephone-type modular plug. In this patent, the shielded cable includes one or more shielded conductors which are formed by bonding an extremely thin layer of conductive material to the outer surface of an insulated wire. By maintaining an extremely thin layer of conductive material (e.g., 0.0003-0.0004 inch), the shielded conductors can fit and are capable of being terminated in a normal modular plug, resulting in a shielded cordset.
Of course, a shielded cordset requires external connection through one of the contact terminals of the modular plug to a source of ground potential. In the past, this was provided, for example, by grounding the solder post end of one of the plurality of conductors of the mating modular jack. The selected conductor positionally corresponded to the location of the required ground in the cordset.
This technique for grounding shielded cordsets suffers from several deficiencies. One deficiency arises when an EMI (electromagnetic interference) signal of high frequency is present on the shield and needs to be conducted to ground. The narrow contacts and long travel path for such high frequency signals tend to set up undesirable reflections that cause the shield to act as an antenna or radiator. This condition has created a need to find a more effective and efficient way of grounding such high frequency EMI signals.
Another problem arises with electrostatic voltage (ESV). Typically, a high frequency, high current spike is followed by a high voltage, low current spike. The narrow, low-capacity ground path for such spikes increases the possibility of their arcing into adjacent signal conductors in looking for ground. Since such adjacent conductors are normally connected to sensitive low voltage circuitry, such arcing can severely damage such circuitry and must be prevented.
It is towards overcoming these and other problems that the present invention is advanced.